1. Field of the Invention
The present invention relates to an electrophoretic display device and a fabrication method thereof, and more particularly, to an electrophoretic display device including a barrier for preventing a sealant leakage, and a partition wall for preventing a sealant from being leaked when the electrophoretic display device is attached, and a fabrication method thereof.
2. Description of the Related Art
An electrophoretic display device is an image display device characterized in that when a pair of electrodes to which a voltage is applied are immersed in a colloid solution, colloid particles move toward either side of polarities. Unlike a liquid crystal display device, the electrophoretic display device does not use a backlight, and is desirable as a flexible display device for use as electronic paper (electronic book). The electrophoretic display device has many advantages, such as having a broad viewing angle, a high reflectivity, and low power consumption.
The electrophoretic display device is configured to have a structure in which an electrophoretic layer may be interposed between two substrates. One of the two substrates is configured as a transparent substrate while the other substrate is configured as an array substrate with a driving element formed thereon. The electrophoretic display device is configured to display an image in a reflective mode in which light input from the outside of the electrophoretic display device is reflected.
FIG. 1 is a cross-sectional view showing the structure of an electrophoretic display device in a related art. As shown in FIG. 1, the electrophoretic display device 1 includes a first substrate 20, a second substrate 40, a thin film transistor (TFT) as a switching element, a pixel electrode 18 formed on the first substrate 20, a common electrode 42 formed on the second substrate 40, an electrophoretic layer 60 formed between the first substrate 20 and the second substrate 40, and an adhesive layer 56 formed between the electrophoretic layer 60 and the pixel electrode 18.
The TFT includes a gate electrode 11 formed on the first substrate 20, a gate insulating layer 22 with the gate electrode 11 formed thereon disposed on the entire surface of the first substrate 20, a semiconductor layer 13 formed on the gate insulating layer 22, and a source electrode 15 and a drain electrode 16 formed on the semiconductor layer 13. A passivation layer 24 is formed on the source electrode 15 and the drain electrode 16 of the TFT.
The pixel electrode 18 for applying a signal to the electrophoretic layer 60 is formed on the passivation layer 24. In this configuration, a contact hole 28 is formed in the passivation layer 24, and the pixel electrode 18 is connected to the drain electrode 16 of the TFT via the contact hole 28.
A color filter layer 44 and a common electrode 42 are formed on the second substrate 40. The electrophoretic layer 60 is formed on the color filter layer 42, and the adhesive layer 56 is formed on the electrophoretic layer 60. The electrophoretic layer 60 includes capsules 70 filled with white particles 74 and black particles 76. When a signal is applied to the pixel electrode 18, an electric field is generated between the common electrode 42 and the pixel electrode 18. Further, the white particles 74 and the black particles 76 within the capsules 70 are driven to move by an electric force of the electric field, and an image is displayed on the electrophoretic display device.
For example, when a negative (−) voltage is applied to the pixel electrode 18 on the first substrate 20 and a positive (+) voltage is applied to the common electrode 42 on the second substrate 40, the white particles 74 assuming the positive (+) charges move toward the first substrate 20 and the black particles 76 assuming the negative (−) charges move toward the second substrate 40. In this configuration, when light is input from an outer side, i.e., from an upper side of the second substrate 40, the input light is reflected by the black particles 76, and black is displayed on the electrophoretic display device.
Alternatively, when a positive (+) voltage is applied to the pixel electrode 18 on the first substrate 20 and a negative (−) voltage is applied to the common electrode 42 on the second substrate 40, the white particles 74 assuming the positive (+) charges move toward the second substrate 40 and the black particles 76 assuming the negative (−) charges move toward the first substrate 20. In this configuration, when light is input from an outer side, i.e., from an upper side of the second substrate 40, the input light is reflected by the white particles 74, and white is displayed on the electrophoretic display device.
However, the related art electrophoretic display device illustrated in FIG. 1 has the following problems.
First, in a method for fabricating the electrophoretic display device in the related art, it is difficult to attach the first and second substrates.
In the electrophoretic display device of the related art, the first substrate 20 and the second substrate 40 are separately fabricated and further attached by an adhesive layer 56 to be completed. In a detailed configuration, the TFT for driving the unit pixels and the pixel electrode 18 for applying an electric field to the electrophoretic layer are formed on the first substrate 20, the common electrode 42, the color filter layer 44, the electrophoretic layer 60, and the adhesive layer 56 are formed on the second substrate 40 through a separate process, and then the first substrate 20 and the second substrate 40 are attached.
However, since the unit pixels of the electrophoretic display device are normally formed to have a small size of approximate 150 micrometers in width and length, it is very difficult in the related art to align the electrophoretic layer to precisely fit into the desired size. When the electrophoretic layer is aligned, if the first substrate 20 with the electrophoretic layer 60 and the TFT formed thereon is not precisely aligned, an electric field may not be properly transferred to the electrophoretic particles, therefore causing a driving signal error.
Second, the fabrication process of the method for fabricating the electrophoretic display device in the related art is complicated.
The first substrate 20 and the second substrate 40 are separately fabricated through different processes, transferred by a transfer unit, and further attached through an attaching process. As a result, the first substrate 20 and the second substrate 40 are not formed in an in-line manner in the fabrication process.
Third, when the first substrate 20 and the second substrate 40 are attached, static electricity is generated and causes a defective initial arrangement of the electrophoretic particles.
The common electrode 42, the color filter layer 44 and the electrophoretic layer 60 are formed on the second substrate 40, and the adhesive layer 56 is applied to the electrophoretic layer 60. Further, to prevent the adhesive strength of the adhesive layer 56 from degrading and an alien material from being attached to the adhesive layer 56, a protection film is attached to the adhesive layer 56. In this configuration, in order to attach the second substrate 40 to the first substrate 20, the protection film must be separated from the second substrate 40. However, electrostatic discharge generated during the process of peeling off the protection film may cause misalignment in the initial arrangement of the electrophoretic particles. The misalignment of the electrophoretic particles due to the electrostatic discharge may generate ripples with a comb pattern during the operation of the electrophoretic display device.
Fourth, the electrophoretic display device in the related art includes the adhesive layer 56 in order to attach the second substrate 40 to the first substrate 20. Since the adhesive layer 56 is positioned between the pixel electrode 56 and the common electrode 42, it hinders an electric field in acting on the electrophoretic particles. Further, a process for sealing the edges of the electrophoretic display device with a sealant is performed in order to prevent moisture or the penetration of an alien material to a display area. In this configuration, the gel state sealant overflows in the sealing process to contaminate the first and second substrates in sealing the first and second substrates. In addition, the design of the external appearance after the sealing operation is degraded.